Significant increase in plasma 4β-hydroxycholesterol concentration in patients after kidney transplantation

Recent advances in the translation of drug metabolism and pharmacokinetics science for drug discovery and development

Drug metabolism and pharmacokinetics (DMPK) is an important branch of pharmaceutical sciences. The nature of ADME (absorption, distribution, metabolism, excretion) and PK (pharmacokinetics) inquiries during drug discovery and development has evolved in recent years from being largely descriptive to seeking a more quantitative and mechanistic understanding of the fate of drug candidates in biological systems. Tremendous progress has been made in the past decade, not only in the characterization of physiochemical properties of drugs that influence their ADME, target organ exposure, and toxicity, but also in the identification of design principles that can minimize drug-drug interaction (DDI) potentials and reduce the attritions. The importance of membrane transporters in drug disposition, efficacy, and safety, as well as the interplay with metabolic processes, has been increasingly recognized. Dramatic increases in investments on new modalities beyond traditional small and large molecule drugs, such as peptides, oligonucleotides, and antibody-drug conjugates, necessitated further innovations in bioanalytical and experimental tools for the characterization of their ADME properties. In this review, we highlight some of the most notable advances in the last decade, and provide future perspectives on potential major breakthroughs and innovations in the translation of DMPK science in various stages of drug discovery and development.

Sensitive UHPLC-MS/MS quantification method for 4β- and 4α-hydroxycholesterol in human plasma for accurate CYP3A phenotyping

4β-Hydroxycholesterol (4β-OHC) is formed by CYP3A4 and CYP3A5 and has drawn attention as an endogenous phenotyping probe for CYP3A activity. However, 4β-OHC is also increased by cholesterol autooxidation occurring in vitro due to dysregulated storage and in vivo by oxidative stress or inflammation, independent of CYP3A activity. 4α-hydroxycholesterol (4α-OHC), a stereoisomer of 4β-OHC, is also formed via autooxidation of cholesterol, not by CYP3A, and thus may have clinical potential in reflecting the state of cholesterol autooxidation. In this study, we establish a sensitive method for simultaneous quantification of 4β-OHC and 4α-OHC in human plasma using ultra-high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). Plasma samples were prepared by saponification, two-step liquid-liquid extraction, and derivatization using picolinic acid. Intense [M+H]+ signals for 4β-OHC and 4α-OHC di-picolinyl esters were monitored using electrospray ionization. The assay fulfilled the requirements of the US Food and Drug Administration guidance for bioanalytical method validation, with a lower limit of quantification of 0.5 ng/mL for both 4β-OHC and 4α-OHC. Apparent recovery rates from human plasma ranged from 88.2% to 101.5% for 4β-OHC, and 91.8% to 114.9% for 4α-OHC. Additionally, matrix effects varied between 86.2% and 117.6% for 4β-OHC, and between 89.5% and 116.9% for 4α-OHC. Plasma 4β-OHC and 4α-OHC concentrations in healthy volunteers, stage 3-5 chronic kidney disease (CKD) patients, and stage 5D CKD patients as measured by the validated assay were within the calibration ranges in all samples. We propose this novel quantification method may contribute to accurate evaluation of in vivo CYP3A activity.

4β-Hydroxycholesterol as an Endogenous Biomarker for CYP3A Activity: Literature Review and Critical Evaluation

A number of cytochrome P450 (CYP)3A phenotyping probes have been used to characterize the drug interaction potential of new molecular entities; of these, midazolam has emerged as the gold standard. Recently, plasma 4β-hydroxycholesterol (4β-OHC), the metabolite of CYP3A-mediated cholesterol metabolism, has been championed as an endogenous biomarker for CYP3A, particularly during chronic conditions where CYP3A activity is altered by disease and in long-term treatment studies where midazolam administration is not optimal. Multiple studies in humans have shown that 4β-OHC can qualitatively differentiate among weak, moderate, and potent CYP3A induction when an inducer, typically rifampin, is administered for up to 2 weeks. Conversely, longer durations of CYP3A inhibitor administration (≥1 month) appear to be necessary to differentiate among weak, moderate, and potent CYP3A inhibitors. A number of studies have reported statistically significant linear relationships between 4β-OHC plasma concentrations (and 4β-OHC:cholesterol ratios) and midazolam clearance. However, sufficiently powered studies assessing the ability of 4β-OHC or 4β-OHC:cholesterol ratios to measure CYP3A activity (ie, predictive performance) have not been conducted to date. Additional limitations associated with 4β-OHC phenotyping include inability to detect acute changes in CYP3A activity, uncertainty with regard to its intestinal formation, ambiguity surrounding the role of CYP3A5 in its metabolism, and lack of clarity regarding the role of transporters in its disposition. As such, the data do not support the use of 4β-OHC or 4β-OHC:cholesterol ratios as an endogenous biomarker for CYP3A activity.

Factors involved in phenoconversion of CYP3A using 4β-hydroxycholesterol in stable kidney transplant recipients

BACKGROUND

Phenoconversion is a phenomenon whereby some genotypic extensive metabolizers transiently exhibit drug metabolizing enzyme activity at similar level as that of poor metabolizers. Renal failure is known to decrease CYP3A activity in humans. Indoxyl sulfate, parathyroid hormone (PTH), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α) have been reported to cause CYP3A downregulation in renal failure. We measured plasma concentrations of the above compounds in stable kidney transplant recipients, and evaluated their relations with phenoconversion of CYP3A evaluated by plasma concentration of 4β-hydroxycholesterol, a biomarker of CYP3A activity. Phenoconversion was defined as a genotypic extensive/intermediate metabolizer exhibiting CYP3A activity below the cutoff value that discriminates extensive/intermediate from poor metabolizers.

METHODS

Sixty-three Japanese kidney transplant recipients who underwent transplantation more than 180 days prior to the study were included. Morning blood samples were collected, and CYP3A5 polymorphism as well as plasma concentrations of 4β-hydroxycholesterol, indoxyl sulfate, intact-PTH, IL-6 and TNF-α were determined.

RESULTS

Significantly higher plasma 4β-hydroxycholesterol concentration was observed in recipients with CYP3A5*1 allele (n = 23) compared to those without the allele (n = 40), and the cut-off value was 40.0 ng/mL. Ten recipients with CYP3A5*1 allele exhibited CYP3A activity below 40.0 ng/mL (phenoconversion). Only plasma indoxyl sulfate concentration was significantly higher in recipients with CYP3A phenoconversion compared to those without phenoconversion.

CONCLUSIONS

These findings suggest that higher plasma indoxyl sulfate concentration may be involved in CYP3A phenoconversion. Dose adjustment of drugs metabolized by CYP3A may be needed in patients with CYP3A5*1 allele and high blood indoxyl sulfate.

Recovery of CYP3A Phenotype after Kidney Transplantation

End-stage renal disease impairs drug metabolism via cytochrome P450 CYP3A; however, it is unclear whether CYP3A activity recovers after kidney transplantation. Therefore, the aim of this study was to evaluate the change in CYP3A activity measured as 4β-hydroxycholesterol (4βOHC) concentration after kidney transplantation. In total, data from 58 renal transplant recipients with 550 prospective 4βOHC measurements were included in the study. One sample per patient was collected before transplantation, and 2-12 samples per patient were collected 1-82 days after transplantation. The measured pretransplant 4βOHC concentrations ranged by >7-fold, with a median value of 22.8 ng/ml. Linear mixed-model analysis identified a 0.16-ng/ml increase in 4βOHC concentration per day after transplantation (P < 0.001), indicating a regain in CYP3A activity. Increasing estimated glomerular filtration rate after transplantation was associated with increasing 4βOHC concentration (P < 0.001), supporting that CYP3A activity increases with recovering uremia. In conclusion, this study indicates that CYP3A activity is regained subsequent to kidney transplantation.

Pretransplant 4β-hydroxycholesterol does not predict tacrolimus exposure or dose requirements during the first days after kidney transplantation

AIMS

The CYP3A metric 4β-hydroxycholesterol (4βOHC) has been shown to correlate with tacrolimus steady-state apparent oral clearance (CL/F). Recently, pretransplant 4βOHC was shown not to predict tacrolimus CL/F after transplantation in a cohort of renal recipients (n = 79). The goal of the current study was determine whether these findings could be validated in a substantially larger cohort.

METHODS

In a retrospective analysis of 279 renal recipients, tacrolimus trough concentrations (C0), daily dose, haematocrit and other relevant covariates were registered every day for the first 14 days after transplantation. 4βOHC and cholesterol were quantified on plasma collected immediately pretransplant using liquid chromatography tandem-mass spectrometry. Patients were genotyped for CYP3A5*1 and CYP3A4*22.

RESULTS

A total of 3551 tacrolimus C0 concentrations were registered. In a linear mixed model for the 14-day period, determinants of tacrolimus C0 were CYP3A5 genotype, haematocrit, age and weight (overall R²  = 0.179). Determinants of daily dose were CYP3A5 genotype, age, methylprednisolone dose, tacrolimus formulation, ALT and estimated glomerular filtration rate (overall R²  = 0.242). Considering each of the first 5 days separately, 4βOHC had a limited effect on tacrolimus C0 on day 3 only (-1.00 ng ml^-1 per ln, P = 0.035) but not on any other day, and no effect on dose or C0/dose. During the first 5 days, haematocrit and age, which were previously established as determinants of tacrolimus disposition under steady-state conditions, never explained more than 17.7% of between-subject variability in tacrolimus C0/dose.

CONCLUSIONS

The CYP3A metric 4βOHC cannot be used to predict tacrolimus dose requirements in the first days after transplantation.

The CYP3A biomarker 4β-hydroxycholesterol does not improve tacrolimus dose predictions early after kidney transplantation

AIMS

Tacrolimus is a cornerstone in modern immunosuppressive therapy after kidney transplantation. Tacrolimus dosing is challenged by considerable pharmacokinetic variability, both between patients and over time after transplantation, partly due to variability in cytochrome P450 3A (CYP3A) activity. The aim of this study was to assess the value of the endogenous CYP3A marker 4β-hydroxycholesterol (4βOHC) for tacrolimus dose individualization early after kidney transplantation.

METHODS

Data were obtained from 79 adult kidney transplant recipients who contributed a total of 625 4βOHC measurements and 1999 tacrolimus whole blood concentrations during the first 2 months after transplantation. The relationships between 4βOHC levels and individual estimates of tacrolimus apparent plasma clearance (CL/F_plasma ) at different time points after transplantation were investigated using scatterplots and population pharmacokinetic modelling.

RESULTS

There was no significant correlation between pre-transplant 4βOHC levels and tacrolimus CL/F_plasma the first week (r = 0.19 [95% CI -0.03-0.40]) or between 4βOHC and tacrolimus CL/F_plasma 1 week (r = 0.20 [-0.11-0.47]), 4 weeks (r = 0.21 [-0.07-0.46]) or 2 months (r = 0.24 [-0.03-0.48]) after transplantation (P ≥ 0.06). In the population analysis, time-varying 4βOHC was not a statistically significant covariate on tacrolimus CL/F_plasma , neither in terms of absolute values (P = 0.11) nor in terms of changes from baseline (P = 0.17). 4βOHC values increased between 1 week and 2 months after transplantation (median change +57% [IQR +22-83%], P < 0.001), indicating increasing CYP3A activity. Contradictorily, tacrolimus CL/F_plasma decreased over the same period (median change -13% [IQR -3 to -26%], P < 0.001).

CONCLUSIONS

4βOHC does not appear to have a clinical potential to improve individualization of tacrolimus doses early after kidney transplantation.

Perspective: 4β-hydroxycholesterol as an emerging endogenous biomarker of hepatic CYP3A

A key goal in the clinical development of a new molecular entity is to quickly identify whether it has the potential for drug-drug interactions. In particular, confirmation of in vitro data in the early stage of clinical development would facilitate the decision making and inform future clinical pharmacology study designs. Plasma 4β-hydroxycholesterol (4β-HC) is considered as an emerging endogenous biomarker for cytochrome P450 3A (CYP3A), one of the major drug metabolizing enzymes. Although there are increasing reports of the use of 4β-HC in academic- and industry-sponsored clinical studies, a thorough review, summary and consideration of the advantages and challenges of using 4β-HC to evaluate changes in CYP3A activity has not been attempted. Herein, we review the biology of 4β-HC, its response to treatment with CYP3A inducers, inhibitors and mixed inducer/inhibitors in healthy volunteers and patients, the association of 4β-HC with other probes of CYP3A activity (e.g. midazolam, urinary cortisol ratios), and present predictive pharmacokinetic models. We provide recommendations for studying hepatic CYP3A activity in clinical pharmacology studies utilizing 4β-HC at different stages of drug development.

An Exposure-Response Modeling Approach to Examine the Relationship Between Potency of CYP3A Inducer and Plasma 4β-Hydroxycholesterol in Healthy Subjects

The objectives of this analysis were to establish the exposure-response relationship between plasma rifampicin and 4β-hydroxycholesterol (4βHC) concentration and to estimate the effect of weak, moderate, and potent CYP3A induction. Plasma rifampicin and 4βHC concentration-time data from a drug-drug interaction study with rifampicin 600 mg were used for model development. An indirect response model with an effect compartment described the relationship between rifampicin and 4βHC concentrations. The model predicted that the equilibration t_1/2 and 4βHC t_1/2 were 72.8 and 142 hours, respectively. EM₅₀ and E_max of rifampicin induction were 32.6 μg and 8.39-fold, respectively. The population PK-PD model was then used to simulate the effects of rifampicin 10, 20, and 100 mg on plasma 4βHC for up to 21 days, in which rifampicin 10, 20, and 100 mg were used to represent weak, moderate, and strong inducers, respectively. The model-predicted median (5th, 95th percentiles) 1.13 (1.04, 1.44)-, 1.28 (1.10, 1.71)-, and 2.10 (1.45, 3.49)-fold increases in plasma 4βHC after 14-day treatment with rifampicin 10, 20, and 100 mg, respectively. A new drug candidate can likely be classified as a weak, moderate, or strong inducer if baseline-normalized plasma 4βHC increases by <1.13-, 1.13- to 2.10-, or >2.10-fold, respectively, after 14 days of dosing.

Use of 4β-hydroxycholesterol in animal and human plasma samples as a biomarker for CYP3A induction

Background: 4β-hydroxycholesterol (4βHC) has recently been proposed as a potential endogenous biomarker for CYP3A activity. Developing bioanalytical assays for 4βHC is challenging for several reasons, including endogenous background levels in plasma; the presence of free and ester forms; the inherent lack of MS sensitivity; and the presence of multiple positional isomers. Results: Bioanalytical assays in mouse, rat, dog and human plasma were adapted and modified from a previous published human plasma assay for 4βHC by using alkaline de-esterification, picolinic derivatization, a surrogate analyte (d7-4βHC) in authentic matrices and chromatographic conditions that showed good separation from isobaric, positional isomers. Conclusion: These assays were applied to multiple studies and demonstrated potential applications of 4βHC as a CYP3A biomarker across preclinical and clinical settings.

CYP3A5 polymorphism affects the increase in CYP3A activity after living kidney transplantation in patients with end stage renal disease

AIMS

It has been reported that cytochrome P450 (CYP)3A activity increases significantly in patients with end stage renal disease (ESRD) after kidney transplantation, with wide interindividual variability in the degree of increase. The aim of this study was to evaluate the influence of CYP3A5 polymorphism on the increase in CYP3A activity after living kidney transplantation, by measuring the plasma concentration of 4β-hydroxycholesterol.

METHODS

This prospective study recruited 22 patients with ESRD who underwent a first living kidney allograft transplantation, comprising 12 patients with CYP3A5*1 allele (CYP3A5*1/*1 or *1/*3) and 10 patients without CYP3A5*1 allele (CYP3A5*3/*3).

RESULTS

No significant difference in estimated glomerular filtration rate over time was observed between patients with the CYP3A5*1 allele and patients without the CYP3A5*1 allele, suggesting that the degrees of recovery in renal function after living kidney transplantation were similar in the two groups. However, plasma concentrations of 4β-hydroxycholesterol on days 90 (57.1 ± 13.4 vs. 39.5 ± 10.8 ng ml(-1)) and 180 (55.0 ± 14.5 vs. 42.4 ± 12.6 ng ml(-1)) after living kidney transplantation were significantly higher in the presence of the CYP3A5*1 allele than in the absence of the CYP3A5*1 allele [P = 0.0034 (95% confidence interval of difference 6.55, 28.6) and P = 0.043 (95% confidence interval of difference 0.47, 24.8), respectively], suggesting that CYP3A activity may increase markedly associated with recovery of renal function in patients with the CYP3A5*1 allele.

CONCLUSIONS

These findings suggest that the presence of the CYP3A5*1 allele contributes to marked elevation of CYP3A activity associated with recovery of renal function after kidney transplantation.